The provision of deck structures is now described with reference to a bridge although it should be appreciated that the same apparatus and method may be used to effect with respect to other load bearing structures such as underpasses, underground stations roofs or the like and therefore the description relating to use for bridges should be interpreted in a non-limiting manner.
There is an increasing demand to be able to provide new facilities and structures without affecting existing surface facilities such as rail tracks, roads or the like. Until recently the construction of a bridge would have required construction to be done from the surface using conventional construction techniques and involving considerable disruption and risk to the surface facility, and/or it may be necessary to make expensive temporary diversions of the surface facility to allow the structure to be constructed.
Alternatively the bridge can be constructed more or less complete at a separate location and then slid in to position at a relatively quiet period of use of the existing road or rail services. However, this requires installation in advance of foundations in the form of slide paths, the closure of the rail or road, complete removal of materials and subsequent reinstatement.
Other techniques for forming a deck to allow a new facility to be formed underneath include the jacking of a concrete box structure into position. However these box structures tend to be very large and so a large site is required to allow the structures to be formed adjacent to the bridge which can be expensive. Furthermore the size of these box structures means that large scale excavation needs to be performed to allow the cavities of a required size to be formed to receive the box structures and the jacking forces needed to move large boxes are very great.
It is also known to create advance support structures so as to form a canopy of tubes which act as a partial support structure but these are not capable of supporting the facility loads without provision of internal support arches as excavation is undertaken inside the canopy.
However none of the prior art methods and apparatus allow the decking structure to be formed in an efficient manner.